Seasonal psychopathology was studied in three samples on archival data. Drug abusers (N=? 760) were tested at the Addiction Research Center in Baltimore, MD the time of recruitment using the SCL-90, Addiction Severity Index, and the Shipley Institute of Living Scale for Measuring Intellectual Impairment. Drug abusers showed more psychopathology such as on depression in summer than in other seasons of the year. A mentally ill sample (N=588) tested at the time of admission to the Friends Hospital in Philadelphia with supervision by R. Lipman using the SCL-90 and other tests of depression such as the Hamilton and Beck Depression. This group also showed greater psychopathology, particularly depression, in the summer months rather than other seasons of the year. Researchers at the Patuxent Institution obtained the incidence of rule infractions within 45 months yielding a total of 5383 infractions. More infractions occurred during the hot summer months as might be predicted from the Anderson's heat-aggression hypothesis.